Trailer brakes are required and/or recommended in a number of different towing situations. For instance, if the tow vehicle has a gross vehicle weight rating (GVWR) over a certain amount, if the trailer has a certain number of axles, or if the trailer exceeds a predetermined weight, then trailer brakes may be appropriate. Trailer brakes can sometimes be useful in situations where the combined weight of the tow vehicle and the trailer warrants an extra set of brakes to help bring the vehicle and trailer to a stop in a quick but stable manner.
Some of the more common types of trailer brakes include surge brakes, electric brakes and, more recently, electric-over-hydraulic (EOH) brakes. Surge brake systems are typically non-electronically controlled systems that generally have a hydraulic piston mounted in the tongue of the trailer so that when the vehicle stops, the forward momentum or inertia of the trailer applies pressure on the piston and engages it. The hydraulic piston is coupled to the trailer brakes, which are typically of the drum or disc variety, and activates them in proportion to the amount of inertial engagement that it experiences. Thus, surge brake systems can generally operate without an electrical connection to the tow vehicle, although one may be needed for other features.
Electric brake systems, on the other hand, are electronically controlled systems that generally operate with the assistance of a magnet-driven actuating lever and require an electrical connection to the tow vehicle in order to receive a control signal. The control signal can include a voltage- and/or current-controlled signal that is proportional to a driver braking intent (DBI). The control signal causes a magnet inside of each brake to become energized, which in turn moves an actuating lever that applies the brake. In most cases, electric brake systems are used with drum brakes.
EOH brake systems are typically electronically controlled systems that drive a closed hydraulic system located on the trailer. More specifically, electronic control signals can be used to turn on a hydraulic pump, which in turn builds pressure for braking. Both disc and drum brakes can be used with most EOH brake systems.